This invention relates to a heat exchanger capable of being effectively used for heat exchange of liquid metalxe2x80x94water system conducted in, for example, a liquid-metal cooled reactor in which a high-temperature heating medium and a low-temperature heating medium are not allowed to contact each other, and more particularly to a heat exchanger adapted to conduct heat exchange via an intermediate heating medium chemically inactive with respect to both the high-temperature heating medium and low-temperature heating medium.
In a liquid-metal cooled reactor using, for example, liquid sodium as a coolant, heat exchange is carried out between a sodium system in which high-temperature sodium is circulated and a water-vapor system. In such a heat exchanger, when the sodium and water contact each other due to damage to a heat exchanger tube, both the sodium and water react with each other violently to get into danger of causing a disaster to occur.
As a means for preventing the sodium and water from immediately contacting each other even when damage to a heat exchanger tube occurs, a method of conducting heat exchange via a stable substance, which reacts with neither the sodium nor water, is proposed in, for example, Japanese Patent Laid-Open No. 53-131394A/1978.
In a heat exchanger concretely proposed in the above-described prior art, a heat exchanger tube is molded in the form of a double tube structure having an outer tube and an inner tube, and water (low-temperature heating medium) is passed through the inner tube with sodium (high-temperature medium) passed through a space on the outer side of an outer circumference of the outer tube. An annular portion between the inner tube and the outer tube is filled with a stable substance (intermediate heating medium) reacting with neither water nor sodium, for example, mercury, via which heat exchange is conducted.
According to the prior art heat exchanger described above, it has the effect of preventing owing to the presence of the intermediate heating medium the sodium and water from contacting each other immediately even when one of the outer tube and the inner tube of the doubly formed heat exchanger tube is damaged. However, since a clearance between the inner tube and the outer tube in the double tube structure is comparatively narrow, the possibility that the inner tube and the outer tube be damaged simultaneously is large. Furthermore, since the quantity of the intermediate heating medium flowing through the annular clearance is small, the possibility that the double tube structure is damaged to cause the sodium and water to contact each other cannot necessarily be eliminated sufficiently.
Moreover, since all the heat exchanger tubes are formed to double tube structures, the construction of the heat exchanger becomes complicated, and the manufacturing cost becomes high. In addition, when a certain doubly formed heat exchanger tube is damaged, it is necessary to examine all of the heat exchanger tubes one by one for the purpose of identifying the damaged heat exchanger tube, so that the speedy detection of a damaged heat exchanger tube cannot be carried out.
An object of the present invention is therefore to provide a heat exchanger having an intermediate heating medium, capable of reducing more greatly the possibility that sodium and water contact each other directly than the above-described prior art heat exchanger in which an outer tube and an inner tube are formed to a double tube structure with a clearance between the outer tube and the inner tube filled with an intermediate heating medium, having a simple heat exchanger tube structure as compared with the double tube structure, and capable of reducing the manufacturing cost.
Another object of the present invention is to provide a heat exchanger having an intermediate heating medium, capable of detecting and identifying a damaged outer tube or inner tube simply and speedily.
The heat exchanger having an intermediate heating medium according to the present invention includes a multiplicity of inner tubes disposed in a shell of a heat exchanger. A low-temperature heating medium flows in these inner tubes and a high-temperature heating medium flows in the shell. These inner tubes are divided into a plurality of groups each of which has a plurality of inner tubes. The plural inner tubes constituting one group are disposed in one outer tube, and an intermediate heating medium chemically inactive with respect to both the high-temperature heating medium and low-temperature heating medium and excellent in heat transferring performance is passed through each outer tube.
According to the heat exchanger of the present invention of such a structure, a multiplicity of inner tubes are divided into groups so that each group has, for example, 3 to 4 inner tubes, and one group having 3 to 4 inner tubes is housed simply in one outer tube. Therefore, this heat exchanger is structurally simple and can reduce the manufacturing cost as compared with the prior art heat exchanger having a double tube structure in which one outer tube and one inner tube are paired with each other.
Since around 3 to 4 inner tubes are disposed in one outer tube, it is unnecessary that a clearance between the outer tube and the inner tubes be formed as narrowly as that between the outer tube and the inner tube of the prior art double tube structure. Further, the interior of the outer tube can be filled with a large quantity of intermediate heating medium. Therefore, the possibility that the high-temperature heating medium (for example, sodium) and low-temperature heating medium (for example, water) contact each other can be reduced to an extremely low level even when any inner tube or the outer tube should be damaged.
Furthermore, since the intermediate heating medium having an excellent heat transferring performance is not only packed but also constantly circulated in a fluidized state in the interior of the outer tube, the performance of the intermediate heating medium of transferring heat from the high-temperature heating medium to the low-temperature heating medium is not substantially spoiled.
When any of the inner tube or the outer tube should be damaged to cause the low-temperature heating medium in the inner tube to leak into the outer tube, or the high-temperature heating medium in the outside of the outer tube to leak into the outer tube, it is necessary that the damage be detected speedily to thereby identify the damaged tube. To meet this requirement, leakage detectors capable of detecting in every outer tube the high-temperature heating medium or low-temperature heating medium leaking into the intermediate heating medium flowing out of the outer tube are provided in a preferred embodiment of the present invention. For example, when the leakage of the low-temperature heating medium into the intermediate heating medium flowing out of one specific outer tube is detected, it is possible to ascertain owing to the provision of these leakage detectors that one of the group of inner tubes in this outer tube is damaged. Therefore, the detection and identification of a damaged tube can be carried out speedily as compared with those carried out in the case where a multiplicity of inner tubes are examined one by one.
In a more preferred embodiment of the present invention, a partition tube is disposed on the inner side of an inner circumference of each outer tube to retain a clearance between the partition tube and the outer tube by positioning spacers between these tubes so that the intermediate heating medium can flow also through the clearance. Thus, even when the outer tube should be damaged, a danger of occurrence of direct contact of the high-temperature heating medium with the outer circumferences of the inner tubes can be further reduced owing to the partition tube disposed on the inner side of the outer tube. This structure serves as a desirable structure for reliably preventing, especially, in a heat exchanger of sodiumxe2x80x94water system a danger of occurrence of the contact of the high-temperature heating medium and water with each other which causes a disaster to occur.